1. Field of the Invention
The present invention relates to a control apparatus and control method for a hybrid vehicle. In particular, the present invention relates to a technique for starting an engine selectively using an electric motor which generates the driving force for the vehicle or using a starter motor which is a motor dedicated for starting the engine, in accordance with the state of the vehicle.
2. Description of Related Art
Conventionally, hybrid vehicles which carry electric motors as power sources for driving the vehicles in addition to engines are known. As kinds of hybrid vehicles, there are parallel hybrid vehicles in which an electric motor is used as an assisting driving source for assisting the output of the engine. These parallel hybrid vehicles perform various controls, for example, when the vehicle accelerates, the electric motor assists the output of the engine, and when the vehicle decelerates, the electric motor generates electric power by deceleration regeneration to charge a battery, etc. Therefore, it is possible to constantly maintain electrical energy (the remaining battery charge) in the battery and to respond to demands made by the driver on the vehicle. For example, Japanese Unexamined Patent Application, First Publication No. Hei 7-123509 discloses such a control technique.
In the hybrid vehicle, it is not only possible to start the engine using a starter motor dedicated for starting the engine, but also it is possible to start the engine using a driving motor for running the vehicle.
However, in conventional hybrid vehicles, when starting the engine, the selection of the starter motor or the driving motor has not been appropriately performed while taking into consideration the protection of various devices and parts in the hybrid vehicles.
Moreover, in the conventional hybrid vehicles, when starting the engine, the selection of the starter motor or the driving motor has not been appropriately performed in consideration of the case where drivers wish to start the engine quickly.
The object of the present invention is to provide a controlling apparatus and method for a hybrid vehicle in which the selection of the starter motor or the driving motor can be appropriately performed to start the engine while taking into consideration the protection of various devices and parts in the hybrid vehicle.
Another object of the present invention is to provide a controlling apparatus and method for a hybrid vehicle in which the selection of the starter motor or the driving motor can be appropriately performed for starting the engine when the driver wishes to start the engine quickly.
In order to achieve the above object, the control apparatus according to the first aspect of the present invention comprises an engine start controller which starts the engine when an engine start is requested. The engine start controller starts the engine using the electric motor if the temperature of the electric motor or the power drive unit is less than a predetermined value, and the engine start controller starts the engine using the starter motor if the temperature of the electric motor or the power drive unit is no less than the predetermined value.
Similarly, the control method according to the first aspect of the present invention comprises determining whether the temperatures of the electric motor and the power drive unit are respectively less than a predetermined values when an engine start is requested; starting the engine using the electric motor in the case where the temperature of the electric motor or the power drive unit is less than a predetermined value; and starting the engine using the starter motor in the case where the temperature of the electric motor or the power drive unit is no less than the predetermined value.
The starter motor is designed to have a maximum rotational speed (for example, 200 r.p.m.) which is just sufficient for starting the engine. In contrast, the electric motor for generating the driving force of the vehicle can output a torque much higher than that of the starter motor, and also has a wider speed range so as to correspond to the whole speed range of the engine. Also, the engine can be started more smoothly and silently when the starting operation is performed at a higher rotational speed for the structural reasons of the engine, etc. Therefore, in the control apparatus and method according to the first aspect, when an engine start is requested, if the vehicle is in a normal state, that is, if the temperatures of the electric motor and the power drive unit are respectively less than a predetermined values, the engine start controller starts the engine using the electric motor which can drive the engine at a high rotational speed (for example, about 2000 r.p.m.). However, if at least one of the temperatures of the electric motor and the power drive unit is no less than the predetermined values, the engine start controller starts the engine using the starter motor, instead of using the electric motor.
That is, if at least one of the temperatures of the electric motor and the power drive unit reaches a temperature which may cause a breakdown or a shortening of the life time of the electric motor or the power drive unit, the driving source for starting the engine is changed from the electric motor to the starter motor. Therefore, according to the first aspect of the present invention, it is possible to appropriately select one of the starter motor and the electric motor in consideration of protection of the electric motor and the power drive unit of the hybrid vehicle.
The control apparatus according to the second aspect of the present invention comprises an engine start controller which starts the engine when an engine start is requested, and the engine start controller starts the engine using the electric motor if the temperature of the power storage unit is within a predetermined temperature range. In contrast, the engine start controller starts the engine using the starter motor if the temperature of the power storage unit is not within the predetermined temperature range.
Similarly, the control method according to the second invention comprising determining whether the temperature of the power storage unit is within a predetermined temperature range when an engine start is requested; starting the engine using the electric motor in the case where the temperature of the power storage unit is within a predetermined temperature range; and starting the engine using the starter motor in the case where the temperature of the power storage unit is not within the predetermined temperature range.
In this second aspect of the present invention, when an engine start is requested, if the vehicle is in a normal state, that is, if the temperature of the power storage unit is within a predetermined temperature range in which the electric motor can start the engine, the engine start controller starts the engine using the electric motor. However, if the temperature of the power storage unit is not within the predetermined temperature range, the engine start controller starts the engine using the starter motor instead of using the electric motor.
That is, when the temperature of the power storage unit is a temperature which may cause a shortening of the life time of the power storage unit if the engine is started using the electric motor, the driving source for starting the engine is changed from the electric motor to the starter motor. Therefore, according to the second aspect, it is possible to appropriately select one of the starter motor and the electric motor in consideration of protection of the power storage unit of the hybrid vehicle.
The control apparatus according to the third aspect of the present invention comprises an engine start controller which starts the engine when an engine start is requested, the engine start controller starts the engine using the electric motor if a contactor is connecting the power drive unit to the power storage unit, and the engine start controller starts the engine using the starter motor if the contactor is not connecting the power drive unit to the power storage unit.
Similarly, the control method for a hybrid vehicle comprises determining whether the contactor is connecting the power drive unit to the power storage unit when an engine start is requested; starting the engine using the electric motor in the case where the contactor is connecting the power drive unit to the power storage unit; and starting the engine using the starter motor in the case where the contactor is not connecting the power drive unit to the power storage unit.
The state in which the contactor is not connecting the power drive unit to the power storage unit includes, for example, the state in which the contactor is being turned off because the precharging of the power drive unit by the power storage unit has not been completed. In such a case, electric power is not being supplied to the electric motor, and the electric motor cannot be used for starting the engine. However, even in such a case, if the driver wishes to start the engine before the completion of the precharging, because the driving source for starting the engine is automatically changed from the electric motor to the starter motor by the engine start controller, it is possible to rapidly start the engine without waiting for the completion of the precharging. Therefore, according to the third aspect of the present invention, the starting of the engine can be performed in accordance with the demand of the driver.
Furthermore, the state in which the contactor is not connecting the power drive unit to the power storage unit includes the state in which the contactor is broken. Even in such a case, the driving source for starting the engine is automatically changed from the electric motor to the starter motor by the engine start controller. Therefore, according to the third aspect of the present invention, even in the state where the electric motor does not work because of a breakdown of the contactor, it is possible to start the engine and to drive the vehicle only by the engine.